Essay on leeuwenhoek

Leeuwenhoek's microscopes were simple magnifying glasses comprised of single spherical or biconvex lens that were mounted amidst two copper, brass or silver plates. The size of the plates matched the modern microscopic slides, . about 1/3 inches. The object that was subjected to the examination was raised, lowered, or rotated by threaded screws attached to the plate. His device also included one of the first mechanical micromanipulation systems. However, Hooke had already accomplished this with a touch of differentiation. It was a possibility that Leeuwenhoek must have understood early that the shallow depth of field of strong microscopic lenses had ruled out focusing on microorganisms by hand. Like modern objective lenses, his lenses were extremely small with short focal lengths of 1-2 millimeters. There was requirement with the lenses; it was a need to consign them close to the eyes, and adequate practice and good eyesight were mandatory factors for their usage. The plates were carved up to provide adequate grasp between the eyebrow and cheek like a jeweller's monocle loupe. Following a standard scientific procedure, the plates were held in a horizontal position with the threaded stem used as a handle peeping away from the nose.

When a patient has cancer and is given high doses of chemotherapy, the chemotherapy kills the cancer cells but also the normal cells in the bone marrow. This means that the patient cannot produce blood cells. So before the patient is treated with chemotherapy, he or she can undergo a bone marrow harvest in which stem cells are removed from the bone marrow by using a needle which is inserted into the pelvis (hip bone). Alternatively, if stem cells cannot be used from the patient then they can be harvested from a matching donor. After the chemotherapy treatment the patient will have a bone marrow transplant in which the stem cells are transplanted back into the patient through a drip, usually via a vein in the chest or the arm. These transplanted stem cells will then find their way back to the bone marrow and start to produce healthy blood cells in the patient. Therefore the therapeutic use of stem cells in bone marrow transplants is very important as it allows some patients with cancer to undergo high chemotherapy treatment. Without this therapeutic use of stem cells, patients would only be able to take low doses of chemotherapy which could lower their chances of curing the disease.

One aspect of his meticulous painting technique was Vermeer's choice of pigments. [31] He is best known for his frequent use of the very expensive ultramarine ( The Milkmaid ), and also lead-tin-yellow ( A Lady Writing a Letter ), madder lake ( Christ in the House of Martha and Mary ), and vermilion . He also painted with ochres , bone black and azurite . [32] The claim that he utilized Indian yellow in Woman Holding a Balance [33] has been disproven by later pigment analysis. [34]